WO2020178497A1

WO2020178497A1 - Color and infrared image sensor

Info

Publication number: WO2020178497A1
Application number: PCT/FR2020/050337
Authority: WO
Inventors: Camille DUPOIRON; Benjamin BOUTHINON
Original assignee: Isorg
Priority date: 2019-03-01
Filing date: 2020-02-21
Publication date: 2020-09-10
Also published as: EP3931873B1; EP3931873A1; US11930255B2; JP7486512B2; JP2022523404A; TW202101783A; US20220141399A1; CN113785397A; KR20210129710A; FR3093376A1; FR3093376B1

Abstract

The present disclosure relates to a color and infrared image sensor (1) comprising a silicon substrate (10), MOS transistors (16) formed in the substrate and on the substrate, first photodiodes (2) formed at least partially in the substrate, a photosensitive layer (26) covering the substrate, and color filters (34), the photosensitive layer being interposed between the substrate and the color filters. The image sensor further comprises first and second electrodes (22, 28) on either side of the photosensitive layer and delimiting second photodiodes (4) in the photosensitive layer, the first photodiodes being configured to absorb the electromagnetic waves of the visible spectrum and of a first portion of the infrared spectrum, the photosensitive layer being configured to absorb the electromagnetic waves of the visible spectrum and to allow the passing of the electromagnetic waves of said first portion of the infrared spectrum.

Description

DESCRIPTION

COLOR AND INFRARED IMAGE SENSOR

The present patent application claims the priority of the French patent application FR19 / 02157 which will be considered as an integral part of the present description.

Technical area

[0001] The present application relates to an image sensor or electronic imager.

Prior art

[0002] Image sensors are used in many fields, in particular in electronic devices thanks to their miniaturization. Image sensors are found either in human-machine interface applications or in image-taking applications.

[0003] For certain applications, it is desirable to have an image sensor allowing simultaneous acquisition of a color image and an infrared image. Such an image sensor is called a color and infrared image sensor in the remainder of the description. An example of application of a color and infrared image sensor relates to the acquisition of an infrared image of an object on which is projected a structured infrared pattern. Areas of use for such image sensors include automobiles, drones, smartphones, robotics and augmented reality systems.

[0004] The phase during which the pixel collects charges under the action of incident radiation is called the integration phase of a pixel. The integration phase is generally followed by a reading phase during which a measurement of the quantity of charges collected by the pixel is carried out. Several constraints are to be taken into account for the design of a color and infrared image sensor. First, the resolution of the acquired color images should not be lower than that obtained with a conventional color image sensor.

[0006] Second, for certain applications, it may be desirable for the image sensor to be of the global shutter type, also called Global Shutter, that is to say implementing an image acquisition process in in which the beginnings and ends of the pixel integration phases are simultaneous. This may be the case in particular for the acquisition of an infrared image of an object onto which a structured infrared pattern is projected.

Thirdly, it is desirable that the size of the pixels of the image sensor is as small as possible. Fourth, it is desirable that the fill factor of each pixel, which corresponds to the ratio between the area, in top view, of the area of the pixel actively participating in the capture of the incident radiation and the total area, with a view to above, of the pixel, or as large as possible.

[0008] It can be difficult to design a color and infrared image sensor which satisfies all of the constraints described above.

Summary of the invention

[0009] One embodiment overcomes all or part of the drawbacks of the color and infrared image sensors described above.

[0010] According to one embodiment, the resolution of the color images acquired by the color and infrared image sensor is greater than 2560 ppi, preferably greater than 8530 ppi. [0011] According to one embodiment, the method for acquiring an infrared image is of the Global Shutter type.

[0012] According to one embodiment, the size of the pixels of the color and infrared image sensor is less than 10 μm, preferably less than 3 μm.

[0013] According to one embodiment, the fill factor of each pixel of the color and infrared image sensor is greater than 50%, preferably greater than 80%.

One embodiment provides a color and infrared image sensor comprising a silicon substrate, MOS transistors formed in the substrate and on the substrate, first photodiodes formed at least partly in the substrate, a photosensitive layer covering the substrate and color filters, the photosensitive layer being interposed between the substrate and the color filters. The image sensor further comprises first and second electrodes on either side of the photosensitive layer and delimiting second photodiodes in the photosensitive layer, the first photodiodes being configured to absorb electromagnetic waves of the visible spectrum and of a first part of the infrared spectrum and the photosensitive layer being configured to absorb the electromagnetic waves of the visible spectrum and to pass the electromagnetic waves of said first part of the infrared spectrum.

[0015] According to one embodiment, the image sensor further comprises an infrared filter, the color filters being interposed between the photosensitive layer and the infrared filter, the infrared filter being configured to pass the electromagnetic waves of the visible spectrum , to pass the electromagnetic waves of said first part of the infrared spectrum and to block the electromagnetic waves of at least a second part of the infrared spectrum between the visible spectrum and the first part of the infrared spectrum.

[0016] According to one embodiment, the image sensor further comprises a matrix of lenses interposed between the photosensitive layer and the infrared filter.

[0017] According to one embodiment, the image sensor further comprises, for each pixel of the color image to be acquired, at least first, second and third subpixels each comprising one of the second photodiodes, the one of the first photodiodes, and one of the color filters, the color filters of the first, second and third subpixels allowing electromagnetic waves to pass through different frequency ranges of the visible spectrum.

[0018] According to one embodiment, for each pixel of the color image to be acquired, the second electrode is common to the first, second and third sub-pixels.

According to one embodiment, the image sensor further comprises, for each pixel of the color image to be acquired, at least a fourth sub-pixel comprising one of the second photodiodes and one of the filters of color, the color filter of the fourth subpixel being configured to block electromagnetic waves of the visible spectrum and to pass electromagnetic waves in a third part of the infrared spectrum between the visible spectrum and the first part of the infrared spectrum, the photosensitive layer being configured to absorb electromagnetic waves in said third part of the infrared spectrum.

[0020] According to one embodiment, the image sensor further comprises, for each first, second and third sub-pixel, a read circuit connected to the second photodiode and to the first photodiode.

According to one embodiment, the read circuit is configured to transfer first electrical charges generated in the first photodiode to a first electrically conductive track and configured to transfer second charges generated in the second photodiode to the first electrically conductive track or a second electrically conductive track.

According to one embodiment, the first photodiodes are arranged in rows and columns and the read circuits are configured to control the generation of the first charges during the first simultaneous time intervals for all the first photodiodes of the image sensor .

[0023] According to one embodiment, the second photodiodes are arranged in rows and in columns and the read circuits are configured to control the generation of the second charges during second simultaneous time intervals for all the second photodiodes of the image sensor or shifted in time from one row of second photodiodes to the other.

According to one embodiment, the read circuits are configured to control a first integration phase for the first photodiodes having a first duration and to control a second integration phase for the second photodiodes having a second duration different from the first duration.

[0025] According to one embodiment, each read circuit comprises at least a first MOS transistor mounted as a follower, the second photodiode having a first electrode connected directly to the gate of the first MOS transistor and the second photodiode having a second electrode connected to the gate of the first MOS transistor, or to the gate of a second MOS transistor mounted as a follower, via a third MOS transistor.

[0026] According to one embodiment, the photosensitive layer is made of organic materials and / or contains quantum dots.

Brief description of the drawings

These characteristics and advantages, as well as others, will be explained in detail in the following description of particular embodiments given without limitation in relation to the accompanying figures, including:

[0028] FIG. 1 is an exploded perspective view, partial and schematic, of an embodiment of a color and infrared image sensor;

[0029] Figure 2 is a sectional view, partial and schematic, of the image sensor of Figure 1 illustrating an embodiment of the electrodes of the image sensor;

[0030] Figure 3 is a sectional view, partial and schematic, of the image sensor of Figure 1 illustrating another embodiment of the electrodes;

[0031] FIG. 4 is an electrical diagram of an embodiment of a circuit for reading a sub-pixel of the image sensor of FIG. 1;

[0032] FIG. 5 is an electrical diagram of another embodiment of the read circuit;

[0033] FIG. 6 is an electrical diagram of another embodiment of the read circuit;

[0034] FIG. 7 is an electrical diagram of another embodiment of the read circuit; FIG. 8 is an electrical diagram of another embodiment of the read circuit;

FIG. 9 is an electrical diagram of another embodiment of the read circuit;

FIG. 10 is a timing diagram of signals of an embodiment of a method of operating the image sensor having the read circuit of FIG. 4;

FIG. 11 is a timing diagram of signals of another embodiment of a method of operating the image sensor having the read circuit of FIG. 4;

FIG. 12 is a timing diagram of signals of an embodiment of a method of operating the image sensor having the read circuit of FIG. 9; and

[0040] FIG. 13 is a timing diagram of signals of an embodiment of a method of operating the image sensor having the read circuit of FIG. 9.

Description of embodiments

The same elements have been designated by the same references in the various figures. In particular, the structural and / or functional elements common to the different embodiments may have the same references and may have identical structural, dimensional and material properties. For the sake of clarity, only the elements useful for understanding the embodiments described have been shown and are detailed. In particular, the use made of the image sensors described below has not been detailed.

In the following description, when reference is made to absolute position qualifiers, such as the terms "front", "rear", "top", "bottom", "left", "right", etc., or relative, such as the terms "above", "below", "upper", "lower", etc., or to orientation qualifiers, such as the terms "horizontal", "vertical", etc., reference is made, unless otherwise specified, to the orientation of the figures or to an image sensor in a normal position of use. Unless otherwise specified, the expressions "approximately", "approximately", "substantially", and "of the order of" mean within 10%, preferably within 5%.

Unless otherwise specified, when referring to two elements connected together, this means directly connected without any intermediate element other than conductors, and when referring to two elements connected or coupled together, it means that these two elements can be directly linked (connected) or linked through one or more other elements. In addition, a signal which alternates between a first constant state, for example a low state, denoted "0", and a second constant state, for example a high state, denoted "1", is called "binary signal". The high and low states of different binary signals of the same electronic circuit can be different. In practice, the binary signals may correspond to voltages or currents which may not be perfectly constant in the high or low state. In addition, it is considered here that the terms "insulator" and "conductor" mean respectively "electrically insulating" and "electrically conductive".

The transmittance of a layer corresponds to the ratio between the intensity of the radiation leaving the layer and the intensity of the radiation entering the layer. In the remainder of the description, a layer or a film is said to be opaque to radiation when the transmittance of the radiation through the layer or the film is less than 10%. In the remainder of the description, a layer or a film is said to be transparent to radiation when the transmittance of the radiation through the layer or film is greater than 10%. In the remainder of the description, the refractive index of a material corresponds to the refractive index of the material for the range of wavelengths of the radiation picked up by the image sensor. Unless otherwise indicated, the refractive index is considered to be substantially constant over the range of wavelengths of the useful radiation, for example equal to the average of the index of refraction over the range of wavelengths of the radiation picked up by the beam. image sensor.

In the remainder of the description, visible light is called electromagnetic radiation whose wavelength is between 400 nm and 700 nm and infrared radiation is called electromagnetic radiation whose wavelength is between 700 nm and 1 mm. In infrared radiation, one distinguishes in particular the near infrared radiation, the wavelength of which is between 700 nm and 1.4 μm.

One pixel of an image corresponds to the unitary element of the image captured by an image sensor. When the optoelectronic device is a color image sensor, it generally comprises for each pixel of the color image to be acquired at least three components which each acquire a light radiation substantially in a single color, that is, that is, in a wavelength range less than 100nm (eg, red, green and blue). Each component can include at least one photodetector.

Figure 1 is an exploded perspective view, partial and schematic, and Figure 2 is a sectional view, partial and schematic, of an embodiment of a color and infrared image sensor 1. The image sensor 1 comprises a matrix of first photon sensors 2, also called photodetectors, suitable for picking up an infrared image, and a matrix of second photodetectors 4, suitable for picking up a color image. The matrices of photodetectors 2 and 4 are associated with a matrix of read circuits 6 carrying out the measurement of the signals picked up by the photodetectors 2 and 4. By read circuit is meant a set of read, address and control transistors. of the pixel or sub-pixel defined by the corresponding photodetectors 2 and 4.

In the image sensor 1, the matrix of color photodetectors 4 covers the matrix of infrared photodetectors 2. For each pixel of the color image to be acquired, the sub-pixel SPix of the image sensor 1 is called the part of the image sensor 1 comprising the photodetector 4 enabling the acquisition of light radiation in a restricted part of the visible radiation of the image to be acquired.

FIGS. 1 and 2 show four SPix sub-pixels. For the sake of clarity, only certain elements of the image sensor 1 present in figure 2 are shown in figure 1. The image sensor 1 comprises from bottom to top in figure 2:

a semiconductor substrate 10 comprising an upper face 12, preferably planar;

for each sub-pixel SPix, at least one doped semiconductor region 14 formed in the substrate 12 and forming part of the infrared photodiode 2;

electronic components 16 of the read circuits 6 located in the substrate 10 and / or on the face 12, a single component 16 being represented by sub-pixel SPix in the figure

2; a stack 18 of insulating layers covering face 12, conductive tracks 20 being located on stack 18 and between the insulating layers of stack 18;

for each sub-pixel SPix, an electrode 22 resting on the stack 18 and connected to the substrate 10, to one of the components 16 or to one of the conductive tracks 20 by a conductive via 24;

an active layer 26 covering all the electrodes 22 and covering the stack 18 between the electrodes 22;

for each sub-pixel SPix, an electrode 28 resting on the active layer 26 and connected to the substrate 10, to one of the components 16 or to one of the conductive tracks 20 by a conductive via 30;

an insulating layer 32 covering all the electrodes 28 and covering the active layer 26 between the electrodes 28;

for each sub-pixel SPix, a color filter 34 covering the insulating layer 32;

for each sub-pixel SPix, a microlens 36 covering the color filter 34;

an insulating layer 38 covering the microlenses 36; and a filter 40 covering the insulating layer 36.

The SPix sub-pixels can be divided into rows and columns. In the present embodiment, each sub-pixel SPix has, in a direction perpendicular to the face 12, a square or rectangular base with sides varying from 0.1 µm to 100 µm, for example equal to about 3 µm. However, each SPix subpixel can have a base of a different shape, for example hexagonal.

In the present embodiment, the active layer

26 is common to all the SPix sub-pixels of image sensor 1. The active zone of each color photodetector 4 corresponds to the zone in which the majority of the incident radiation is absorbed and converted into an electrical signal by the color photodetector 4 and corresponds substantially to the part of the active layer 26 situated between the lower electrode 22 and the upper electrode 28.

According to one embodiment, each infrared photodetector 2 is suitable for picking up electromagnetic radiation in a range of wavelengths between 400 nm and 1100 nm. According to one embodiment, the active layer 26 is suitable for capturing electromagnetic radiation in a range of wavelengths between 400 nm and 700 nm, that is to say for absorbing only visible light. According to another embodiment, the active layer 26 is suitable for capturing electromagnetic radiation in a range of wavelengths between 400 nm and 920 nm, that is to say visible light and part of the near infrared. . The photodetectors can be made of organic materials The photodetectors can correspond to organic photodiodes (OPD, standing for Organic Photodiode) or to organic photoresistors. In the remainder of the description, it is considered that the photodetectors correspond to photodiodes.

The filter 40 is adapted to allow visible light to pass, to allow the part of the infrared radiation to pass over the range of infrared wavelengths of interest for the acquisition of the infrared image and to block the rest of the rest of the incident radiation and in particular the rest of the infrared radiation outside the range of infrared wavelengths of interest. According to one embodiment, the range of infrared wavelengths of interest may correspond to a range of 50 nm centered on the expected wavelength of infrared radiation, for example. centered on the 940 nm wavelength or centered on the 850 nm wavelength. The filter 40 can be an interference filter and / or include absorbent and / or reflective layers.

The color filters 34 can correspond to blocks of colored resin. Each color filter 34 is adapted to pass infrared radiation, for example at a wavelength between 700 nm and 1 mm, and, for at least some of the color filters, to pass a range of wavelengths visible light. For each pixel of the color image to be acquired, the image sensor can comprise a sub-pixel SPix whose color filter 34 is adapted to allow only blue light to pass, for example in the wavelength range. from 430 nm to 490 nm, one SPix sub-pixel whose color filter 34 is adapted to pass only green light, for example in the wavelength range 510 nm to 570 nm and one sub-pixel SPix whose color filter 34 is adapted to allow only red light to pass, for example in the wavelength range of 600 nm to 720 nm.

According to one embodiment, the active layer 26 is adapted to capture electromagnetic radiation in a range of wavelengths between 400 nm and 700 nm, that is to say to absorb only visible light. The color filters 34 can then be distributed according to a Bayer matrix. As a result, for each sub-pixel SPix, the color photodetector 4 of the sub-pixel only captures the part of the visible light which has passed through the color filter 34 of the sub-pixel.

According to another embodiment, the active layer 26 is adapted to capture electromagnetic radiation in a range of wavelengths between 400 nm and 920 nm, that is to say visible light and a part close infrared. In this case, one of the color filters 34 is adapted to allow only infrared radiation to pass and to block visible light. One of the color photodiodes 4 then acts as a near infrared photodiode. This can be advantageous for acquiring color images, especially in low light. The infrared radiation picked up by the infrared photodiodes 2 corresponds to a range of wavelengths different from the infrared radiation picked up by the color photodiode 4 playing the role of photodiode for the near infrared.

According to one embodiment, the semiconductor substrate 10 is made of silicon, preferably of monocrystalline silicon. The substrate may be of the silicon on insulator or SOI (acronym for Silicon On Insulator) type comprising a stack of a layer of silicon on an insulating layer. According to one embodiment, the electronic components 16 comprise transistors, in particular metal-oxide gate field effect transistors, also called MOS transistors. The infrared photodiodes 2 are inorganic photodiodes, preferably made of silicon. Each infrared photodiode 2 comprises at least the doped silicon region 14 which extends into the substrate 10 from the face 12. According to one embodiment, the substrate 10 is undoped or lightly doped with a first type of conductivity, for example example of type P and each region 14 is a doped region, of the type of conductivity opposite to the substrate 10, for example of type N. The depth of each region 14, measured from the face 12, may be between 1 μm and 12 μm . The infrared photodiode 2 can correspond to a pinched photodiode. Examples of pinched photodiodes are described in particular in US Pat. No. 6,677,656. They are for example photodiodes separated by deep isolation trenches to facilitate the collection of charges generated at depth due to radiation in the near infrared. The conductive tracks 20 and the conductive vias 24, 30 can be made of a metallic material, for example silver (Ag), aluminum (Al), gold (Au), copper (Cu), nickel (Ni), titanium (Ti) and chromium (Cr). The conductive tracks 20 and the conductive vias 24, 30 can have a monolayer or multilayer structure. Each insulating layer of the stack 18 can be made of an inorganic material, for example of silicon oxide (SiCy) or a silicon nitride (SiN).

Each electrode 22, 28 is at least partially transparent to the light radiation it receives. Each electrode 22, 28 may be of a conductive and transparent material, for example of conductive and transparent oxide or TCO (acronym for Transparent Conductive Oxide), of carbon nanotubes, of graphene, of a conductive polymer, of a metal, or as a mixture or an alloy of at least two of these compounds. Each electrode 22, 28 can have a single or multi-layered structure.

Examples of TCO suitable for the production of each electrode 22, 28 are indium-tin oxide (ITO, from the English Indium Tin Oxide), aluminum-zinc oxide (AZO, from English Aluminum Zinc Oxide) gallium-zinc oxide (GZO, from English Gallium Zinc Oxide), titanium nitride (TiN), molybdenum oxide (M0O ₃₎ and tungsten oxide ( WO ₃₎ . An example of a conductive polymer suitable for making each electrode 22, 28 is the polymer known under the name PEDOT: PSS, which is a mixture of poly (3, 4) -ethylenedioxythiophene and sodium polystyrene sulfonate and polyaniline, also called PAni. Examples of metals suitable for making each electrode 22, 28 are silver, aluminum, gold, copper, nickel, titanium and chromium. An example of a multilayer structure suitable for making each electrode 22, 28 is a multilayer AZO and silver AZO / Ag / AZO type structure.

The thickness of each electrode 22, 28 may be between 10 nm and 5 μm, for example of the order of 30 nm. In the case where the electrode 22, 28 is metallic, the thickness of the electrode 22, 28 is less than or equal to 20 nm, preferably less than or equal to 10 nm.

Each insulating layer 32, 38 can be made of fluoropolymer, in particular the fluoropolymer sold under the name Cytop by the company Bellex, of polyvinylpyrrolidone (PVP), of polymethyl methacrylate (PMMA), of polystyrene (PS) , in parylene, in polyimide (PI), in acrylonitrile butadiene styrene (ABS), in poly (ethylene terephthalate) (PET, abbreviation polyethylene terephthalate), in poly (ethylene naphthalate) (PEN, abbreviation for polyethylene naphthalate), cyclic olefin polymers (COP, acronym for Cyclo Olefin Polymer), polydimethylsiloxane (PDMS), a photolithography resin, epoxy resin, acrylate resin or a mixture of at least two of these compounds. As a variant, each insulating layer 32, 38 may be made of an inorganic dielectric, in particular of silicon nitride, of silicon oxide or of aluminum oxide (Al ₂ O ₃₎ . Aluminum oxide can be deposited by depositing thin atomic layers (ALD, acronym for Atomic Layer Deposition). The maximum thickness of each insulating layer 32, 38 may be between 50 nm and 2 μm, for example of the order of 100 nm.

[0063] The active layer 26 can comprise small molecules, oligomers or polymers. They can be organic or inorganic materials, in particular quantum dots. The active layer 26 may comprise an ambipolar semiconductor material, or a mixture of an ambipolar material. N-type semiconductor and of a P-type semiconductor material, for example in the form of superposed layers or of an intimate mixture at the nanometric scale so as to form a volume heterojunction. The thickness of the active layer 26 may be between 50 nm and 2 μm, for example of the order of 200 nm.

Examples of P-type semiconductor polymers suitable for producing the active layer 26 are poly (3-hexylthiophene) (P3HT), poly [N-9 '-heptadecanyl- 2, 7-carbazole-alt- 5, 5- (4, 7-di-2-thienyl-2 ', l', 3 '- benzothiadiazole)] (PCDTBT), poly [(4, 8-bis- (2-ethylhexyloxy) -benzo [1 , 2-b; 4, 5-b '] dithiophene) -2, 6-diyl- alt- (4- (2-ethylhexanoyl) -thieno [3, 4-b] thiophene)) -2, 6-diyl] (PBDTTT-C), poly [2-methoxy-5- (2-ethyl-hexyloxy) -1, 4-phenylene-vinylene] (MEH-PPV) or poly [2, 6- (4, 4-bis - (2-ethylhexyl) -4H-cyclopenta [2, 1-b; 3, 4-b '] dithiophene) -alt-

4.7 (2,1,3-benzothiadiazole)] (PCPDTBT).

Examples of N-type semiconductor materials suitable for producing the active layer 26 are fullerenes, in particular C60, [6, 6] -phenyl-C _6i- methylbutanoate ([60] PCBM), [6, 6] -phenyl-C _7i methyl butanoate ([70] PCBM), the diimide perylene, zinc oxide (ZnO) or nanocrystals allow the formation of quantum dots (English quantum dots).

The active layer 26 can be interposed between first and second interface layers, not shown. Depending on the mode of polarization of the photodiode, the interface layers facilitate the collection, the injection or the blocking of the charges from the electrodes in the active layer 26. The thickness of each interface layer is preferably between 0 , 1 nm and 1 ym. The first interface layer aligns the output work of the adjacent electrode with the electron affinity of the acceptor material used in the active layer 26. The first interface layer can be made of cesium carbonate (CSCO ₃₎ , of metal oxide, in particular of zinc oxide (ZnO), or of a mixture of at least two of these compounds. The first interface layer may comprise a self-assembled monomolecular layer or a polymer, for example polyethyleneimine, ethoxylated polyethyleneimine, poly [(9,9- bis (3 '- (N, N-dimethylamino) propyl) -2, 7-fluorene) -alt-2, 7-

(9,9-dioctylfluorene)]. The second interface layer makes it possible to align the output work of the other electrode with the ionization potential of the donor material used in the active layer 26. The second interface layer can be made of copper oxide (CuO ), in nickel oxide (NiO), in vanadium oxide (V ₂ O ₅ ), in magnesium oxide (MgO), in tungsten oxide (WO ₃ ), in molybdenum oxide (M0O ₃₎ , in PEDOT: PSS or a mixture of at least two of these compounds.

The microlenses 36 are of micrometric size.

In the present embodiment, each SPix sub-pixel comprises a microlens 36. As a variant, each microlens 36 can be replaced by another type of micrometric-sized optical element, in particular a micrometric-sized Fresnel lens, a micrometer-sized gradient index lens or micrometer-sized diffraction grating. The microlenses 36 are converging lenses each having a focal length f of between 1 µm and 100 µm, preferably between 1 µm and 10 µm. According to one embodiment, all of the microlenses 36 are substantially identical.

The microlenses 36 can be made of silica, PMMA, a positive photosensitive resin, PET, PEN, COP, PDMS / silicone, or epoxy resin. The microlenses 36 can be formed by creeping blocks of a photosensitive resin. The microlenses 36 can besides being formed by molding on a layer of PET, PEN, COP, PDMS / silicone or epoxy resin.

According to one embodiment, the layer 38 is a layer which follows the shape of the microlenses 36. The layer 38 may be obtained from an optically transparent adhesive (OCA, acronym for Optically Clear Adhesive), in particular a liquid optically transparent adhesive (LOCA, acronym for Liquid Optically Clear Adhesive), or a material with a low refractive index, or an epoxy / acrylate glue, or a film of a gas or a gas mixture, for example of l 'air. Preferably, when the layer 38 conforms to the shape of the microlenses 36, the layer 38 is of a material having a low refractive index, lower than that of the material of the microlenses 36. The layer 38 may be of a filling material which is a transparent non-adhesive material. According to another embodiment, the layer 38 corresponds to a film which is applied against the array of microlenses 36, for example an OCA film. In this case, the contact zone between the layer 38 and the microlenses 36 can be reduced, for example limited to the tops of the microlenses. The layer 38 can then be composed of a material having a higher refractive index than in the case where the layer 38 conforms to the microlenses 36. According to another embodiment, the layer 38 corresponds to an OCA film which is applied against. the array of microlenses 36, the adhesive having properties which allow the film 38 to completely or substantially completely conform to the surface of the microlenses.

Depending on the materials considered, the method of forming at least some layers of the image sensor 1 may correspond to a so-called additive method, for example by direct printing of the material composing the organic layers at the desired locations, in particular in the form of sol-gel, for example by inkjet printing, heliography, screen printing, flexography, spray coating (in English spray coating) or depositing of drops (in English drop-casting). Depending on the materials considered, the process for forming the layers of the image sensor 1 may correspond to a so-called subtractive process, in which the material composing the organic layers is deposited on the entire structure and in which the unused portions are then removed, for example by photolithography or laser ablation. In addition, depending on the layers and the materials considered, the material making up the active layer 26 is deposited over the entire structure and is not partially removed, the pitch of the photodiodes then being obtained by the position of the electrodes 22 and 28. Depending on the material considered, the deposition on the entire structure can be carried out for example by liquid, by cathodic sputtering or by evaporation. They may in particular be processes of the spin coating, spray coating, heliography, slot-die coating, blade coating, flexography or screen printing type. When the layers are metallic, the metal is, for example, deposited by evaporation or by cathodic sputtering on the whole of the support and the metallic layers are delimited by etching.

Advantageously, at least some of the layers of the image sensor 1 can be produced by printing techniques. The materials of these layers described above can be deposited in liquid form, for example in the form of conductive and semiconductor inks using inkjet printers. The term “materials in liquid form” is understood here also to mean gel materials which can be deposited by printing techniques. Annealing steps are optionally provided between the deposits of the various layers, but the annealing temperatures may not exceed 150 ° C., and the deposition and any annealing may be carried out at atmospheric pressure.

Figure 3 is a sectional view of the image sensor 1 illustrating another embodiment of the arrangement of the electrodes of the color photodiodes 4. In the present embodiment, the electrode 28 is common to each color photodiode. 4 of the pixel. In addition, the electrode 28 can be common to all the pixels of the same row of pixels. Via 30 may then not be present for each sub-pixel of the pixel and be provided in areas not corresponding to sub-pixels, for example at the periphery of the pixel. Only the electrode 22 is delimited for each sub-pixel SPix.

FIG. 4 represents the simplified electric diagram of an embodiment of the read circuit 6-1 associated with the color photodiode 4 and with the infrared photodiode 2 of a sub-pixel SPix.

The read circuit 6-1 comprises a MOS transistor in follower assembly 60, in series with a selection MOS transistor 62, between two terminals 64, 66. Terminal 64 is connected to a source of a reference potential high VDD in the case where the transistors making up the read circuit are N-channel MOS transistors, or with a low reference potential, for example ground, in the case where the transistors making up the read circuit are MOS transistors to channel P. The terminal 66 is connected to a conductive track 68. The conductive track 68 can be connected to all the sub-pixels of a same column and be connected to a current source 69 which is not part of the circuit. 6-1 reading of the subpixel. The gate of transistor 62 is intended to receive a signal SEL for selecting the sub-pixel. The gate of transistor 60 is connected to a node FD. The FD node is connected, by a transistor Reset MOS 70, to a terminal for applying a reset potential Vrst, this potential possibly being VDD. The gate of transistor 70 is intended to receive a sub-pixel reset control signal RST, making it possible in particular to reset the node FD substantially to the potential Vrst.

The FD node is connected to the cathode electrode 22 of the color photodiode 4 of the sub-pixel in question via a transfer MOS transistor 72. The anode electrode 28 of the color photodiode 4 of the sub-pixel is connected to a source of a reference potential V_RGB. The gate of transistor 72 is intended to receive a signal TG_RGB for selecting the color photodiode 4 of the sub-pixel. The gate of transistor 60 is also connected to the cathode electrode of infrared photodiode 2 of the subpixel under consideration via a transfer MOS transistor 74. The anode electrode of infrared photodiode 2 of the sub-pixel is connected to a source of a low reference potential GND, for example ground. The gate of transistor 74 is intended to receive a signal TG_IR for selecting the infrared photodiode 2 of the sub-pixel. In the present embodiment, the read circuit 6-1 shown in FIG. 4 comprising five MOS transistors is provided for each sub-pixel. For each row of subpixels, the signals SEL, TR_RGB, TR_IR, RST and the potential V_RGB can be transmitted to all the subpixels of the row. The potential at the FD node referenced with respect to the low reference potential GND is called V_FD. A capacitor can be provided, not shown, one electrode of which is connected to the node FD and the other electrode of which is connected to the source of the low reference potential GND. As a variant, the role of this capacitor can be fulfilled by the stray capacitances present at the node FD. FIG. 5 represents the simplified electric diagram of another embodiment of the read circuit 6-2 associated with the color photodiode 4 and with the infrared photodiode 2 of a sub-pixel. The read circuit 6-2 comprises all the elements of the read circuit 6-1 shown in FIG. 4 with the difference that the transfer transistor 72 is not present, the cathode electrode 22 being directly connected to the gate of the transistor 60 mounted as a follower.

FIG. 6 represents the simplified electric diagram of another embodiment of the read circuit 6-3 associated with the color photodiode 4 and with the infrared photodiode 2 of a sub-pixel. The read circuit 6-3 comprises all the elements of the read circuit 6-1 shown in FIG. 4 and further comprises, for each conductive track 68, an operational amplifier 76 whose inverting input (-) is connected to the track conductor 68, whose non-inverting input (+) is connected to a source of a reference potential Vref and whose output supplies the potential Vrst applied to one of the power terminals of the reset transistor 70. The amplifier operational 76 can be connected to all the reset transistors 70 of the sub-pixels connected to the conductive track 68. The operational amplifier 76 forms a feedback loop which makes it possible to reduce, or even eliminate, the thermal noise of the reset transistor 70 , this noise being usually removed by a reading method implementing a correlated double sampling (CDS, acronym for Correlated Double Sampling).

FIG. 7 represents the simplified electric diagram of another embodiment of the read circuit 6-4 associated with the color photodiode 4 and with the photodiode infrared 2 of a sub-pixel. The read circuit 6-4 comprises all the elements of the read circuit 6-1 shown in FIG. 4 with the difference that the transfer MOS transistor 72 is not present, that the cathode electrode 22 of the color photodiode 4 is connected to the gate of the transistor in the follower circuit 60 and that the read circuit 6-4 further comprises a MOS transistor in the follower circuit 78, in series with a MOS selection transistor 80, between two terminals 82, 84. Terminal 82 is connected to the source of the high reference potential VDD. Terminal 84 is connected to conductive track 68. The gate of transistor 80 is intended to receive a signal SEL ′ for selecting the infrared photodiode 2. The gate of transistor 78 is connected, by a reset MOS transistor 86, to a reset signal. resetting potential Vrst application terminal. The gate of transistor 86 is intended to receive a reset control signal RST ′ of the infrared photodiode 2 making it possible to recharge the photodiode 2 by applying a potential Vrst to the cathode of the infrared photodiode. The gate of transistor 78 is connected to transfer transistor 74.

FIG. 8 represents the simplified electric diagram of another embodiment of the read circuit 6-5 associated with the color photodiode 4 and with the infrared photodiode 2 of a sub-pixel. The read circuit 6-5 comprises all the elements of the read circuit 6-4 represented in FIG. 7 and furthermore comprises the operational amplifier 76 of the read circuit 6-3 represented in FIG. 6 whose inverting input (-) is connected to the conductive track 68, whose non-inverting input (+) is connected to the source of a reference potential Vref and whose output provides the potential Vrst applied to one of the power terminals of the reset transistors 70 and 86. FIG. 9 represents the simplified electric diagram of another embodiment of the read circuit 6-6 associated with the color photodiode 4 and with the infrared photodiode 2 of a sub-pixel. The read circuit 6-6 comprises all the elements of the read circuit 6-4 shown in FIG. 7, with the difference that the selection transistor 80 is connected to a conductive track 88, different from the conductive track 68, and which is connected to a current source 89. In the present embodiment, the color sub-pixels and the infrared sub-pixels are therefore not connected in columns. This makes it possible to implement different reading methods, in particular by the durations of the successive steps of the method, for the color pixels and the infrared pixels.

In general, the reset potentials Vrst, Vrst 'can be common to all the pixels. The potential Vrst is then equal to the potential Vrst '. As an alternative, the reset potentials can be differentiated depending on the column on which the corresponding pixels are read.

FIG. 10 is a timing diagram of the binary signals RST, TG_IR, TG_RGB and SEL, and of the potentials V_RGB and V_FD during an embodiment of a method of operating the image sensor 6-1 shown in FIG. 4. We call t0 to t9 successive instants of an operating cycle. The timing diagram was established by considering that the MOS transistors of read circuit 6-1 are N-channel transistors.

At the instant t0, the signal SEL is in the low state so that the selection transistor 62 is blocked. The cycle includes a reset phase. For this purpose, the RST signal is high so that the reset transistor 70 is on. Signal TG_IR is high so that transfer transistor 74 is on. The charges accumulated in the infrared photodiode 2 are then evacuated to the source of the potential Vrst. Similarly, the signal TG_RGB is high so that the transfer transistor 72 is on. The color photodiode 4 is recharged by injecting charges via the potential source Vrst.

Just before the instant t1, the potential V_RGB is set to a low level. At the instant t1, which marks the start of a new cycle, the signal TG_IR is set low so that the transfer transistor 74 is off and the signal TG_RGB is set to the low state so that the transfer transistor 72 is blocked. An integration phase then begins during which charges are generated in the photodiodes 2 and 4. Just after the instant t1, the signal RST is set low so that the reset transistor 70 is blocked. The potential V_FD is then fixed at a first value VI. Between times t1 and t2, the signal SEL is temporarily set to a high state, so that the potential of the conductive track 68 reaches a value representative of VI which is stored.

At time t2, the potential V_RGB is set to a high level, which stops the collection of charges in the color photodiode 4. Between the times t2 and t3, the signal TG_IR is set to the high state of so that the transfer transistor 74 is on. The charges stored in the infrared photodiode 2 are then transferred to the node FD whose potential V_FD decreases to a value V2. Between times t3 and t4, the signal SEL is temporarily set high, so that the potential of the conductive track 68 reaches a value representative of V2 which is stored. The difference between the values V2 and VI is representative of the quantity of charges collected in the infrared photodiode 2 during the integration phase. Between times t4 and t5, the RST signal is set high so that the reset transistor 70 is on. The potential V_FD then stabilizes substantially at a value V3. Between times t5 and t6, the signal SEL is temporarily set high, so that the potential of the conductive track 68 reaches a value representative of V3 which is stored. Between times t6 and t7, signal TG_RGB is set high so that transfer transistor 72 is on. The charges collected in color photodiode 4 are then transferred to node FD, the potential of which V_FD decreases to a value V4. Between times t7 and t8, the signal SEL is temporarily set high, so that the potential of the conductive track 68 reaches a value representative of V4 which is stored. The difference between the values V4 and V3 is representative of the quantity of charges stored in the color photodiode 4 during the integration phase. The instant t9 marks the end of the cycle and corresponds to the instant t1 of the following cycle. In the present embodiment, the duration of the integration phase of the infrared photodiode 2 is controlled by the transfer transistor 74 while the duration of the integration phase of the color photodiode 4 is controlled by the potential V_RGB. In the present embodiment, the integration phase of the color photodiode 4 has the same duration as the integration phase of the infrared photodiode 2.

This embodiment advantageously makes it possible to carry out a reading method of the Global Shutter type for the acquisition of the color image, in which the integration phases of all the color photodiodes are carried out simultaneously, and a Global Shutter type reading method for acquiring the infrared image, in which the integration phases of all the infrared photodiodes are produced simultaneously.

FIG. 11 is a timing diagram of the binary signals RST, TG_IR, TG_RGB and SEL, and of the potentials V_RGB and V_FD during another embodiment of a method of operating the image sensor 6-1 shown in Figure 5. Compared to the timing diagram shown in Figure 10, the T_IR signal in Figure 11 varies like the T_RGB signal in Figure 10 and the T_RGB signal is not present in Figure 11. In the present embodiment, the duration of the integration phase of the infrared photodiode 2 is controlled by the transfer transistor 74 while the duration of the integration phase of the color photodiode 4 is controlled by the potential V_RGB. Reading is carried out in two stages. A first reading step is performed between times t3 and t4 where the value of color photodiode 4 is read and a second reading step is performed between times t7 and t8 where the sum of the value of color photodiode 4 and the value of infrared photodiode 2 is read. The value of the infrared photodiode 2 is obtained by an operation of subtraction of the two values read. In the present embodiment, the integration phase of the color photodiode 4 is shorter than the integration phase of the infrared photodiode 2. The present embodiment advantageously makes it possible to carry out a reading method of Global type. Shutter for the acquisition of the color image, in which the integration phases of all the color photodiodes are carried out simultaneously, and a Global Shutter type reading method for the acquisition of the infrared image, in which the integration phases of all the infrared photodiodes are carried out simultaneously. FIG. 12 is a timing diagram of the binary signals RST, TG_IR, TG_RGB and SEL, and of the potentials V_RGB and V_FD during another embodiment of a method of operating the image sensor 6-1 shown in FIG. 4. The present operating cycle comprises the same succession of phases as the operating cycle illustrated in FIG. 10, with the difference that the potential V_RGB remains in the low state until an instant tl ', located in the present embodiment between times t1 and t2.

In the present embodiment, for each sub-pixel, the integration phase of the infrared photodiode 2 extends from the instant t1 to the instant t2 and the integration phase of the color photodiode 4 extends from time tl to time tl '. The present embodiment allows the duration of the integration phase of the infrared photodiode to be different from the integration phase duration of the color photodiode. In addition, the present embodiment advantageously makes it possible to carry out a reading method of Global Shutter type for acquiring the color image and a reading method of Global Shutter type for acquiring the infrared image.

FIG. 13 is a timing diagram of the signals RST'_1, RST '_2, RST_1, RST_2, SEL_1, SEL_2 and of the potentials V_RGB_1 and V_RGB_2 during another embodiment of a method of operating the sensor d 'images 6-6 shown in FIG. 9 considering the first and second successive rows of pixels, the signals and potentials associated with the first row of pixels comprising the suffix "_1" and the signals and potentials associated with the second row of pixels comprising the suffix "_2".

As shown in Figure 13, the signals

V_RGB_1 and V_RGB_2 are permanently kept low. The integration phases of the infrared photodiodes of the two rows controlled by the signals TG_IR_1 and TG_IR_2 are carried out simultaneously while the integration phase of the color photodiode of the first row controlled by the signals RST_1 and SEL_1 is shifted in time with respect to the integration phase of the color photodiode of the second row controlled by the signals RST_2 and SEL_2. This makes it possible to implement a reading method of the Global Shutter type for infrared photodiodes and a reading method of the "rolling shutter" type for color photodiodes in which the integration phases of the lines of pixels are time-shifted relative to each other.

Various embodiments and variants have been described. Those skilled in the art will understand that certain features of these various embodiments and variants could be combined, and other variants will be apparent to those skilled in the art. In particular, the read circuits represented in FIGS. 5 to 8 can be implemented with any one of the subpixel structures represented in FIGS. 2 and 3. In addition, the timing diagrams described previously in relation to FIGS. 9 and 10 can also be implemented with the read circuits represented in FIGS. 5 to 8. Finally, the practical implementation of the embodiments and variants described is within the reach of those skilled in the art from the functional indications given above.

Claims

1. Color and infrared image sensor (1) comprising a silicon substrate (10), MOS transistors (16; 60,

62, 70, 72, 74) formed in the substrate and on the substrate, first photodiodes (2) formed at least in part in the substrate, a photosensitive layer (26) covering the substrate and color filters (34), the photosensitive layer being interposed between the substrate and the color filters, the image sensor further comprising first and second electrodes (22, 28) on either side of the photosensitive layer and delimiting second photodiodes (4) in the photosensitive layer, the first photodiodes being configured to absorb the electromagnetic waves of the visible spectrum and of a first part of the infrared spectrum and the photosensitive layer being configured to absorb the electromagnetic waves of the visible spectrum and to pass the electromagnetic waves of said first part of the infrared spectrum, the image sensor comprising, for each pixel of the color image to be acquired, at least first, second and third so us-pixels (SPix) each comprising one of the second photodiodes (4), one of the first photodiodes (2), and one of the color filters (34), the color filters of the first, second and third sub-pixels allowing electromagnetic waves to pass through different frequency ranges of the visible spectrum, the image sensor comprising, for each pixel of the color image to be acquired, at least one fourth sub-pixel (SPix) comprising one second photodiodes (4) and one of the color filters (34), the color filter of the fourth subpixel being configured to block electromagnetic waves of the visible spectrum and to pass electromagnetic waves into a third part of the infrared spectrum between the visible spectrum and the first part of the infrared spectrum, the photosensitive layer (26) being configured to absorb electromagnetic waves in said third part of the infrared spectrum.

2. Image sensor according to claim 1, further comprising an infrared filter (40), the color filters (34) being interposed between the photosensitive layer (26) and the infrared filter, the infrared filter being configured to pass. electromagnetic waves of the visible spectrum, to let the electromagnetic waves of said first part of the infrared spectrum pass and to block the electromagnetic waves of at least a second part of the infrared spectrum between the visible spectrum and the first part of the infrared spectrum.

3. Image sensor according to claim 2, comprising an array of lenses (36) interposed between the photosensitive layer (26) and the infrared filter (50).

4. Image sensor according to any one of claims 1 to 3, wherein, for each pixel of the color image to be acquired, the second electrode (28) is common to the first, second and third sub-pixels (SPix ).

5. Image sensor according to any one of claims 1 to 4, comprising, for each first, second and third sub-pixel (SPix), a read circuit (6-2) connected to the second photodiode (4). and the first photodiode (2).

6. Image sensor according to claim 5, wherein the read circuit (6-2) is configured to transfer first electrical charges generated in the first. photodiode (2) to a first electrically conductive track (68; 88) and configured to transfer second charges generated in the second photodiode (4) to the first electrically conductive track (68) or a second electrically conductive track.

7. Image sensor according to claim 6, wherein the first photodiodes (2) are arranged in rows and columns and wherein the read circuits (6-2) are configured to control the generation of the first charges during the first. simultaneous time intervals for all the first photodiodes (2) of the image sensor.

8. Image sensor according to claim 6 or 7, wherein the second photodiodes (4) are arranged in rows and columns and wherein the read circuits (6-2) are configured to control the generation of the second charges during. second simultaneous time intervals for every second photodiodes of the image sensor or shifted in time from one row of second photodiodes to the other.

9. Image sensor according to any one of claims 6 to 8, wherein the read circuits (6-2) are configured to control a first integration phase for the first photodiodes (2) having a first duration and to control a second integration phase for the second photodiodes (4) having a second duration different from the first duration.

10. Image sensor according to any one of claims 6 to 9, wherein each read circuit (6-2) comprises at least a first MOS transistor (60) mounted as a follower, the second photodiode (4) having a first electrode (22) connected directly to the gate of the first transistor MOS and the second photodiode (2) having a second electrode connected to the gate of the first MOS transistor, or to the gate of a second MOS transistor (78) mounted as a follower, via a third MOS transistor (74 ).

11. Image sensor according to any one of claims 1 to 10, wherein the photosensitive layer (26) is made of organic materials and / or contains quantum dots.